Graphite is a modification of the element carbon, with six hexagonally arranged carbon atoms forming the basic unit of the graphite crystal. Graphite has long been used as lubricant, burn-out material or support material in the production of catalysts. In the production of shaped catalyst bodies, graphite can serve to lubricate the steel tools used and thereby reduce mechanical wear of the molding tools. For such a use, the graphites used are generally selected for their lubricating properties and used in an amount which is required for satisfactory lubrication.
For example, WO 2004/085356 describes the production of a shaped body by mixing an oxidic material with graphite and shaping the resulting mixture to give a shaped body. Further examples of the use of graphite as tabletting aid and/or as lubricant in shaped catalyst production may be found in the documents WO 01/68245, WO 2005/030393, DE-A 10 2005 035 978, EP-A 1 060 792, WO 03/078310, WO 03/78059, DE-A 10 2005 037 678 and EP-A 467 144.
In addition, graphite is also used as burn-out material in order to influence the specific surface area and pore size of a shaped catalyst body. Thus, WO 2008/087116 and DE-A 10 2007 005 606 describe processes for producing a shaped catalyst body, in which graphite is added as shaping aid to a precursor mixture and the mixture formed is shaped to the desired geometry. The shaped catalyst body is subsequently subjected to a heat treatment in which the graphite is converted into compounds which are given off in gaseous form (i.e. CO and/or CO2). The graphite used in the two patent applications serves as pore former and has been removed very completely by burning out in the catalytically active shaped catalyst body.
Carbon-containing materials are also used as support material of catalysts. In organic synthesis, palladium on activated carbon is frequently used for catalytic hydrogenation reactions. Palladium-based catalysts on graphite having a high specific surface area as support material are used for dechlorination and hydrogenation reactions (see, for example, E. Diaz et al., Appl. Catal. 2010, B 99, pages 181-190 or R. F. Bueres, Catal. Today 2010, 150, pages 16-21).
Further hydrogenation catalysts using graphite as support component are described in DE 10 2004 007 499. These hydrogenation catalysts comprise rhenium as active component and are produced by applying a rhenium component to oxidatively pretreated “high surface activated graphite”.
U.S. Pat. No. 4,066,712 claims a catalyst which is present as intercalate of Cr and graphite. The catalyst is used for the reforming of nonaromatic compounds to give products having an increased proportion of aromatics.
DE 4324693 describes the use of fullerene intercalates with Pd, Ru or Fe and their use as catalysts. The catalysts were tested for the example of the hydrogenation of cyclohexene in tetrahydrofuran as solvent.
In the commercial use of catalysts, a further improvement in the economics, in particular an increase of the conversion to the target product, and/or a reduction in the formation of undesirable by-products are of greatest interest.
In view of this background, it was the object of the present invention to provide an improved process for producing shaped metal oxide catalyst bodies, which results, in particular, in shaped catalyst bodies which have a higher activity and/or selectivity compared to catalysts of the prior art.
This object is achieved by the process of the invention and the catalysts which can be obtained thereby.
The increased activity of the catalysts of the invention compared to conventional catalysts makes it possible to carry out the corresponding catalytic processes at lower pressures or temperatures. This fact leads to a considerable cost saving for the plant operator. A temperature decrease in particular leads to a longer operating life of the catalyst since it slows deactivation due to sintering effects, carbonization or the by-products coating the surface. In addition, more active catalysts make it possible to carry out the corresponding reactions at higher space velocities. An equal throughput can therefore be achieved using smaller reactors, which means a considerable reduction in capital costs for a plant operator. A decrease in temperature can additionally lead to a reduction in the amount of by-products. Furthermore, improved selectivity reduces the outlay in terms of apparatus for the removal of by-products and thus the work-up costs for the product.